Magnetic disk apparatus, read/write control method, and controller

ABSTRACT

According to at least one embodiment, a magnetic disk apparatus includes a magnetic disk, a nonvolatile memory, a determination module, a write module, and a read module. The determination module determines whether the off-track write occurs on a first data sector during a write mode. The write module writes first data in the nonvolatile memory if the determination module determines that the off-track write occurs on the first data sector. The read module reads the first data from one of the magnetic disk and the nonvolatile memory based on a determination result of the determination module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2012-020270, filed Feb. 1, 2012,the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic diskapparatus, read/write control method, and controller, which can controlreading and writing with respect to a magnetic disk.

BACKGROUND

In recent years, in the magnetic disk apparatus, a technique for writingdata to the magnetic disk at high density has been developed. Thistechnique is called a shingled write recording method for writing dataso that neighboring tracks on a magnetic disk overlap each other. In theshingled write recording method, since the neighboring tracks overlapeach other, the number of tracks which are recordable per the magneticdisk can be increased, and data can be written at a higher density.

Also, a so-called inter-track interference (ITI) cancellation techniquehas been developed. With this technique, upon reading data which havebeen written to the magnetic disk using the shingled write recordingmethod, noise can be canceled using data written to a track whichneighbors the track currently being read.

While data are written to a given track using the shingled writerecording method, they are unexpectedly written at positions outside thecurrently written track because of influences such as vibration, thuscausing off-track errors. After the off-track error has occurred,processing for writing data (write processing) must be interrupted untilan on-track state, that is, the state where allow data to be written tothe magnetic disk as a result of tracking control.

Since it is difficult to read data which have been written to an area ofthe magnetic disk where an off-track error has occurred, those data mustbe rewritten to the magnetic disk. Furthermore, when data areoverwritten in the area where the off-track error has occurred, theinfluence of magnetic interference on the neighboring tracks oftenbecomes greater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary block diagram showing an example of thearrangement of a magnetic disk apparatus according to a firstembodiment;

FIG. 2 is an exemplary block diagram showing an example of thearrangement of an interface controller in the magnetic disk apparatusaccording to the first embodiment;

FIG. 3 is an exemplary view showing an example of the configuration oftracks on a magnetic disk written by the shingled write recording methodaccording to the first embodiment;

FIG. 4 shows an exemplary sectional view of the tracks shown in FIG. 3and exemplary positions of a read head upon reading these tracksaccording to the first embodiment;

FIGS. 5A, 5B, and 5C are exemplary views showing a data write methodbased on the shingled write recording method upon occurrence of theoff-track error according to the first embodiment;

FIGS. 6A, 6B, and 6C are exemplary views showing a read method of datawritten by the shingled write recording method upon occurrence of theoff-track error according to the first embodiment;

FIGS. 7A, 7B, 7C, and 7D are exemplary views showing a data write methodbased on the shingled write recording method upon occurrence of anoff-track error according to a second embodiment;

FIGS. 8A, 8B, and 8C are exemplary views showing a read method of datawritten by the shingled write recording method upon occurrence of theoff-track error according to the second embodiment;

FIGS. 9A, 9B, and 9C are exemplary views showing a data write methodbased on the shingled write recording method upon occurrence of anoff-track error according to a third embodiment;

FIGS. 10A, 10B, and 10C are exemplary views showing a read method ofdata written by the shingled write recording method upon occurrence ofthe off-track error according to the third embodiment;

FIGS. 11A, 11B, 11C, and 11D are exemplary views showing a data writemethod based on the shingled write recording method upon occurrence ofan off-track error according to a fourth embodiment;

FIGS. 12A, 12B, 12C, and 12D are exemplary views showing a read methodof data written by the shingled write recording method upon occurrenceof the off-track error according to the fourth embodiment;

FIG. 13 is an exemplary view for explaining differences of four modes ofthe shingled write recording method upon occurrence of an off-trackerror according to a fifth embodiment;

FIG. 14 is an exemplary flowchart showing a write processing sequence ofthe shingled write recording method upon occurrence of the off-trackerror according to the fifth embodiment; and

FIG. 15 is an exemplary flowchart showing a read processing sequence ofdata written by the shingled write recording method upon occurrence ofthe off-track error according to the fifth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic disk apparatusincludes a magnetic disk, a nonvolatile memory, a determination module,a write module, and a read module. The magnetic disk includes a firstdata sector, first data being recorded in the first data sector whileneighboring tracks partially overlapping each other. The determinationmodule determines whether off-track write occurs on the first datasector during to mode. The write module writes the first data in thenonvolatile memory if the determination module determines that off-trackwrite occurs on the first data sector. The read module reads the firstdata from one of the magnetic disk and the nonvolatile memory based on adetermination result of the determination module.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

First Embodiment

The first embodiment will be described below with reference to thedrawings.

FIG. 1 is a block diagram showing principal parts of a magnetic diskapparatus according to this embodiment.

As shown in FIG. 1, the magnetic disk apparatus roughly includes ahead-disk assembly (HDA), a head amplifier integrated circuit (to bereferred to as a head amplifier IC hereinafter) 11, and a hard diskcontroller (HDC) 15.

The HDA has a magnetic disk 1 as a recording medium, a spindle motor(SPM) 2, an arm 3 which mounts a head 10, and a voice coil motor (VCM)4. The magnetic disk 1 is rotated by the spindle motor 2. The arm 3 andVCM 4 configure an actuator. The actuator controls to move the head 10mounted on the arm 3 to a designated position on the magnetic disk 1 bydriving the VCM 4.

The head 10 has a write head 10W and read head 10R mounted on a slideras a main body. The write head 10W writes data (write data) to a track200 on the magnetic disk 1 (to be referred to as a write modehereinafter). The read head 10R reads data (read data) recorded in thedata track 200 on the magnetic disk 1 (to be referred to as a read modehereinafter).

Respective blocks shown in FIG. 1 will be described below in signaltransmission orders in the write and read modes.

Functions of the respective blocks in FIG. 1 in the write mode will bedescribed first.

A host system 20 is connected to an interface controller 13 in themagnetic disk apparatus. The host system 20 sends the write data to theinterface controller 13.

The HDC 15 is configured by a 1-chip integrated circuit including theinterface controller 13, a read/write (R/W) channel 12, and amicroprocessor (MPU) 14.

The interface controller 13 is connected to the host system 20, the R/Wchannel 12, the MPU 14, a DRAM 16, and a nonvolatile memory 17. Theinterface controller 13 temporarily stores the write data received fromthe host system 20 in the DRAM 16, and then transfers the write data tothe R/W channel 12 or the nonvolatile memory 17 based on an instructionfrom the MPU. Note that the write data received from the host system 20may be transferred to the R/W channel 12 or the nonvolatile memory 17without being temporarily stored in the DRAM 16.

Although the DRAM 16 and the nonvolatile memory 17 are not included inthe HDC 15, the explanation of the DRAM 16 and the nonvolatile memory 17will be described below.

The DRAM 16 is a volatile memory, which is connected to the interfacecontroller 13, and the DRAM 16 can temporarily store data such as thewrite data transferred from the interface controller 13. The DRAM 16serves as a buffer which temporarily stores the data such as the writedata.

The nonvolatile memory 17 is connected to the interface controller 13.The nonvolatile memory 17 is a high-speed and large-capacity nonvolatilememory. The nonvolatile memory 17 can store the data such as the writedata transferred from the interface controller 13. Note that thenonvolatile memory 17 can store data not temporarily even in a power-OFFstate, unlike data stored in the magnetic disk 1, and may serve as analternate memory of the magnetic disk 1.

The MPU 14 is connected to the interface controller 13 and the R/Wchannel 12. The MPU 14 executes arithmetic processing and the like forthe interface controller 13 and R/W channel 12. The MPU 14 is a maincontroller of a drive, and executes servo control for positioning thehead 10 by controlling the VCM 4.

The R/W channel 12 is connected to the interface controller 13, MPU 14,and head amplifier IC 11. The R/W channel 12 includes a write channelwhich executes signal processing of the write data, and a read channelwhich executes signal processing of the read data. The R/W channel 12performs signal processing (for example, encoding) to write datatransferred from the interface controller 13 using the write channel.The R/W channel 12 sends the encoded write data to the head amplifier IC11.

The head amplifier IC 11 is connected to the head 10 and R/W channel 12.The head amplifier IC 11 has a write driver and a pre-amplifier. Thewrite driver supplies write currents to the write head 10W, according tothe write data output from the R/W channel 12. The write head 10W writesdata to the disk 1 based on the supplied write currents. Note that thepre-amplifier will be described later.

Functions of the respective blocks shown in FIG. 1 in the read mode willbe described below. Note that a description of the same components andfunctions as the contents described above in association with the writemode will not be given.

The pre-amplifier included in the head amplifier IC 11 amplifies a readsignal read by the read head 10R, and transfers the amplified readsignal to the R/W channel 12.

The read channel included in the R/W channel 12 executes processing (forexample, decoding) based on the signal sent from the head amplifier IC11, and sends the decoded signal to the interface controller 13 as readdata.

The interface controller 13 executes, for example, off-trackdetermination based on the read data sent from the R/W channel 12. Also,the interface controller 13 controls the DRAM 16 to temporarily storethe read data sent from the R/W channel 12. Note that the interfacecontroller 13 may send the read data sent from the R/W channel 12 to thehost system 20 without controlling the DRAM 16 to temporarily store theread data.

The interface controller 13 reads the temporarily stored read data fromthe DRAM 16, and sends the read data to the host system 20. Theinterface controller 13 can read data from the nonvolatile memory 17 inplace of reading data from the magnetic disk 1.

Detailed functions of the interface controller 13 will be describedbelow with reference to FIG. 2.

The interface controller 13 includes a write module 21, a read module22, a host controller 23, a DRAM controller 24, a nonvolatile memorycontroller 25, a disk controller 26, and a servo controller 27.

The host controller 23, the DRAM controller 24, the nonvolatile memorycontroller 25, and the disk controller 26 are connected to each othervia an internal data bus 30.

The write module 21, the DRAM controller 24, the nonvolatile memorycontroller 25, and the servo controller 27 are connected to each othervia an internal control bus 28.

The read module 22, the DRAM controller 24, the nonvolatile memorycontroller 25, and the disk controller 26 are connected to each othervia an internal data bus 29.

The host controller 23 and the host system 20, the DRAM controller 24and the DRAM 16, the nonvolatile memory controller 25 and thenonvolatile memory 17, the disk controller 26 and the R/W channel 12,and the servo controller 27 and R/W channel 12 are respectivelyconnected to each other via external buses.

Functions and the like of the interface controller 13 will be distinctlydescribed below in association with the read mode and the write mode,respectively.

Functions and the like of the interface controller 13 in the write modewill be described first.

The host controller 23 sends write data sent from the host system 20 tothe DRAM 16 via the internal bus 30 and DRAM controller 24, so as tostore that write data in the DRAM 16 as buffer data.

The write module 21 includes a write data selector 21 a. The write dataselector 21 a switches write locations of data sent from the host system20 based on occurrence of a write error such as the off-track error.Writable locations include the magnetic disk 1 and the nonvolatilememory 17. The write data selector 21 a selects whether write datastored in the DRAM 16 are to be written in the disk 1 or the nonvolatilememory based on a signal (to be referred to as an off-track detectionsignal hereinafter; to be described in detail later) sent from the servocontroller 27 via the internal control bus 28. The write module 21executes control for writing the write data stored in the DRAM 16 in oneof the disk 1 and the nonvolatile memory via the internal bus 28 basedon the selection result of the write data selector 21 a.

In this embodiment, when the off-track error is detected, the write dataare then transferred to the nonvolatile memory 17 until the off-trackerror ceases to be detected. More specifically, if the write dataselector 21 a selects that the write data are to be written in thenonvolatile memory 17, the write module 21 sends the write data storedin the DRAM 16 to the nonvolatile memory 17 via the internal data bus 30and the nonvolatile memory controller 25.

The off-track detection signal indicates occurrence of the off-trackerror. As will be described later with reference to FIG. 5C, it isassumed that the off-track error is an error of an off-track in adirection of a track which has not been written (recorded) yet by theshingled write recording method. The off-track means that the center ofthe track 200 on the magnetic disk 1 and the center of the write head10W deviate from each other. Whether or not the off-track error hasoccurred is determined by an off-track determination module 27 a.

The servo controller 27 includes the off-track determination module 27a. The servo controller 27 executes processing associated with servodata sent from the R/W channel 12.

The off-track determination module 27 a determines, based on servoinformation (for example, position information of the write head 10W andthe like) included in the servo data, whether or not the off-track errorhas occurred. When the off-track error has occurred, that is, when theoff-track error is detected, the off-track determination module 27 asends the off-track detection signal to the write data selector 21 a.

More specifically, the off-track determination module 27 a determines“NG” based on the servo information if the off-track error has occurred.The off-track determination module 27 a determines “OK” if the off-trackerror does not occur, that is, if the center of the track 200 and thecenter of the write head 10W do not deviate from each other (on-track).In this way, the off-track determination module 27 a may determineoccurrence of the off-track error.

If the off-track determination module 27 a determines that the off-trackerror has occurred, a property of the off-track is stored in the DRAM16, the nonvolatile memory 17, an internal register or SRAM (not shown)of the interface controller 13, or the like. The property of theoff-track includes an address on the magnetic disk 1 which indicates anarea where the off-track error has occurred (off-track address), and/ora data size of the area where the off-track error has occurred. Theoff-track address is, for example, a start address of the area where theoff-track error has occurred, an end address of the area where theoff-track error has occurred, or the like. The property of the off-trackmay be, for example, information as a combination of the start and theend addresses, information as a combination of the start address and thedata size of the area where the off-track error has occurred, or thelike.

Functions and the like of the interface controller 13 in the read modewill be described below.

Initially, a description will be given under the assumption that datawritten in one of the disk 1 and nonvolatile memory 17 is to be read.

The read module 22 reads data from one of the disk 1 and the nonvolatilememory 17, and temporarily stores the read data in the DRAM 16. Morespecifically, the read module 22 sends a read request signal required toread data from the nonvolatile memory 17 or the disk 1 to thenonvolatile memory controller 25 and/or the disk controller 26 via theinternal control bus 29. The nonvolatile memory controller 25 or thedisk controller 26 reads data from the nonvolatile memory 17 or the disk1 based on the read request signal. The nonvolatile memory controller 25or the disk controller 26 sends the read data to the DRAM 16 via theinternal data bus 30. Note that the data read from the nonvolatilememory 17 may be sent to the host system without being stored in theDRAM 16.

Data to be temporarily stored in the DRAM 16 (to be referred to astemporary stored data hereinafter) are data for one round of a trackhaving, for example, a data sector corresponding to a position of theread head 10R on the magnetic disk 1 (to be referred to as a read datasector hereinafter). Data for one round of the track having the readdata sector are those for one round of a track (to be referred to as aneighboring track hereinafter) which neighbors a currently read track(to be referred to as a read track hereinafter) and which was readbefore reading of the read track.

More specifically, the temporary stored data are data corresponding to atrack for one round from a data sector (to be referred to as aneighboring data sector hereinafter) which neighbors the read datasector and is included in the neighboring track to a data sector whichneighbors the read data sector in the read track and was read beforereading of the read data sector.

The DRAM controller 24 stores, for example, the data for one round ofthe neighboring track, in the DRAM 16. After that, the DRAM controller24 sends the temporary stored data stored in the DRAM 16 to the hostsystem 20, so as to maintain a state in which the data for one round ofa track are stored in the DRAM 16, according to new data sent to theDRAM 16.

Note that the read module 22 may temporarily store data read from thenonvolatile memory 17 or the disk 1 in the DRAM 16, in addition, maysend data read from the nonvolatile memory 17 or the disk 1 to the hostsystem 20 via the internal data bus 30.

The following description will be given under the assumption that datawritten in the magnetic disk 1 by the shingled write recording methodare read using an ITI cancellation function.

The shingled write recording method is a method that allows to increasethe capacity of the magnetic disk 1 and that allows to record data onthe magnetic disk 1 at a higher density. With the shingled writerecording method, data can be written in a shingle pattern while closingup track pitches so that neighboring tracks overlap each other to have aplurality of track as a write unit group.

The ITI cancellation function is a function of reading the magnetic disk1 while canceling inter-track interference components (noise) which aregenerated between tracks using data in a data sector in the neighboringtrack (ITI cancellation data) when data written to the magnetic disk 1by the shingled write recording method are to be read. For example, whenthe read data sector is to be read, data in the aforementionedneighboring data sector corresponds to the ITI cancellation data.

Read processing using the ITI cancellation function will be practicallydescribed below with reference to FIG. 2.

The read module 22 includes an ITI cancellation data selector 22 a. TheITI cancellation data are stored in the DRAM 16 and/or the nonvolatilememory 17. The ITI cancellation data selector 22 a selectively reads theITI cancellation data from one of the DRAM 16 and the nonvolatile memory17. The ITI cancellation data selector 22 a transfers the ITIcancellation data to the R/W channel 12. The ITI cancellation dataselector 22 a reads data from the magnetic disk 1 while executing ITIcancellation using the ITI cancellation data.

The ITI cancellation data is data in the neighboring data sector storedin the DRAM 16 or the nonvolatile memory 17. The ITI cancellation dataselector 22 a sends, the ITI cancellation data from one of the DRAM 16and the nonvolatile memory 17, to the R/W channel 12 based on theproperty of the off-track.

The ITI cancellation function as mentioned above is, in FIG. 2, forexample, a function for canceling noise from data of the read datasector using data of the read data sector read from the magnetic disk 1and the ITI cancellation data sent to the R/W channel 12. For example,the noise may be canceled by controlling the R/W channel 12 to subtractthe value of the ITI cancellation data from the value of the data in theread data sector.

The shingled write recording method will be practically described belowwith reference to FIG. 3.

FIG. 3 is assumed a case in which four tracks form one shingled writerecording unit in shingled write recording method. The four tracksinclude a fixed data track on which the fixed data are written, track A,track B, and track C in turn from the upper side of FIG. 3. The fixeddata are those of predetermined repetitive patterns or the like. Notethat a case will be assumed wherein data are written from the outerperiphery side of the magnetic disk 1 toward the inner periphery side.The upper side of FIG. 3 corresponds to the outer periphery side of themagnetic disk 1, and the lower side of FIG. 3 corresponds to the innerperiphery side of the magnetic disk 1. Assuming that data are writtenfrom the inner periphery side of the magnetic disk 1 toward the outerperiphery side, the upper side of FIG. 3 may correspond to the innerperiphery side of the magnetic disk 1, and the lower side of FIG. 3 maycorrespond to the outer periphery side of the magnetic disk 1.

The shingled write recording method in the write mode will be describedfirst.

The write module 21 writes data to the magnetic disk 1 in the order ofthe fixed data track, track A, track B, and track C.

The fixed data are those which are set in advance in the magnetic diskapparatus or the like. That is, the fixed data are written first by theshingled write recording method, and are used to read data in the trackA using the ITI cancellation function in the order of writings by theshingled write recording method. The fixed data track is a data track onwhich the fixed data are written. In FIG. 3, the fixed data track hasdata sectors A′0 to A′3. The fixed data are written in the order fromthe data sectors A′0 to A′3, that is, in turn from the left side to theright side in FIG. 3.

The track A neighbors the fixed data track, and data are written to thetrack A after the fixed data are written to the fixed data track. Dataof the track A are written so that a part of the track A, that is, apart of the upper side of the track A in FIG. 3 overlaps a part of thefixed data track, that is, a part of the lower side of the fixed datatrack in FIG. 3, that is, they are overwritten on a part of the fixeddata. The track A has data sectors A0 to A3, and data of the track A arewritten in turn from the data sectors A0 to A3, that is, in turn fromthe left side to the right side in FIG. 3. Likewise, data of the track Bare written so that a part of the track A overlaps a part of the trackB, as shown in FIG. 3. Also, data of the track C are written so that apart of track B overlaps a part of the track C.

The read processing of data written by the shingled write recordingmethod will be described below with reference to FIG. 3.

The head 10 reads data in the order from the data sectors MO to A′3 inthe fixed data track. After that, the head 10 reads data from the datasectors A0 to A3 in the track A, from the data sectors B0 to B3 in thetrack B, and from the data sectors C0 to C3 in the track C. FIG. 3 showsthat the head 10 moves from the data sectors B1 to B2 in the track B.Note that servo data areas are not shown in FIG. 3.

The head 10 is located on the data sector B1, the data sector B1corresponds to the aforementioned read data sector, and the data sectorA1 corresponds to the neighboring data sector in FIG. 3. In this case,the ITI cancellation data required to read the data sector B1corresponds to the data sector A1.

The configuration between a plurality of tracks written by the shingledwrite recording method and the positions of the head 10 will bedescribed below with reference to FIG. 4.

The upper side of FIG. 4 shows a plurality of tracks on the magneticdisk 1, which correspond to the plurality of tracks written by theshingled write recording method shown in FIG. 3. The lower side of FIG.4 shows sectional views of the plurality of tracks written by theshingled write recording method and corresponding to the upper side ofFIG. 4. These sectional views are used to explain the principle of theshingled write recording method. Note that in FIG. 4, the left side ofFIG. 4 is the outer periphery side of the magnetic disk 1, and the rightside of FIG. 4 is the inner periphery side of the magnetic disk 1.

With reference to the sectional views in FIG. 4, a track A section 41overlaps a fixed data section 40. A part on the inner periphery side ofthe track A section 41 is overwritten by a part on the outer peripheryside of a track B section 42. Likewise, a part on the inner peripheryside of the track B section 42 is overwritten by a part on the outerperiphery side of a track C section 43. In this manner, parts of thetracks A and B are respectively overwritten by parts of the tracks B andC. For this reason, the noise is required to be canceled using the ITIcancellation function upon reading the tracks A and B.

The positions of the head 10 will be described below.

In FIG. 4, reference numerals 44, 45, and 46 respectively denote readranges upon reading data in the tracks A, B, and C. Central positions ofthe read head 10R upon reading data in the tracks A, B, and C arerespectively indicated by central positions P1, P2, and P3.

The read mode will be described below. Initially, data of the track A isread within the range representing by the reference numeral 44 using thepredetermined fixed data as the ITI cancellation data. Data of the trackB is read within the range representing by the reference numeral 45. Inthis case, the already read data of the track A is used as the ITIcancellation data. Likewise, data of the track C is read within therange representing by the reference numeral 46. In this case, thealready read data of the track B is used as the ITI cancellation data.The central position P3 of the read head 10R upon reading data in thetrack C corresponds to the center of the track C section 43. Bycontrast, the central positions P1 and P2 are offset from the centers ofthe track B section 41 and track C section 42 toward the outer peripheryside, so as not to read data in the tracks B and C. In this manner, byoffsetting the central positions P1 and P2, the respective tracks can beread using the ITI cancellation function in the order of data trackswritten by the shingled write recording method.

Write processing upon occurrence of the off-track error will bedescribed below with reference to FIGS. 5A to 5C.

Note that in this embodiment it is assumed that the shingled writerecording method in which the degree of overlap between tracks is low.For this reason, in this case, the aforementioned ITI cancellationfunction need not be used in the read mode. The fixed data trackdescribed with reference to FIGS. 3 and 4 is not shown in FIGS. 5A, 5B,5C, 6A, 6B, 6C, 7A, 7B, 7C, 7D, 8A, 8B, 8C, 9A, 9B, 9C, 10A, 10B, 10C,11A, 11B, 11C, 11D, 12A, 12B, 12C, and 12D for the sake of illustrativeconvenience.

FIG. 5A shows write processing with respect to the track A. Data sectorsA0 and A1 are located between servo area 50 and servo area 51. Likewise,data sectors A2 and A3 are located between the servo area 51 and servoarea 52. Data sectors A4 and A5 are located between the servo area 52and servo area 53. Data sectors A6 and A7 are located between the servoarea 53 and servo area 54.

The write head 10W moves in a direction of an arrow in FIG. 5A, andwrites data in respective data sectors A0 to A9.

Note that as for the determination of the off-track, if the off-trackerror has occurred on the data sectors A0 and A1, this determination ofthe off-track is executed based on servo data in the servo area 51.

FIG. 5B shows write processing with respect to the track B. Althoughthese tracks A and B overlap each other to have a low degree of overlap,they are illustrated without any overlapping for the sake ofillustrative convenience. Also, FIG. 5C and FIGS. 6A, 6B, and 6C to bedescribed later also illustrate tracks without any overlapping due to alow degree of overlap for the sake of illustrative convenience.

FIG. 5B illustrates a case in which the off-track error has occurred onthe data sectors B2 and B3. The data sectors B2 and B3 will be referredto as off-track data sectors hereinafter. After the data sectors B0 andB1, which are to be read prior to the off-track data sectors, are read,read data are sent to the DRAM 16. Next, on the off-track data sectors,the write head 10W (not shown in FIGS. 5A to 5C) moves, as indicated byan arrow 55, thus causing an off-track error. Note that occurrence ofthe off-track error on the off-track data sectors is determined based onservo data in a servo area 57.

If the off-track error has occurred, data to be ten to the magnetic disk1 are written to the nonvolatile memory 17 until the off-track erroroccurs. FIG. 5B illustrates that the off-track error does not occur,that is, a state of the on-track is detected based on the servo data ina servo area 58. A write gate in an interval from the data sectors B2 toB7 is off, and data of the off-track data sectors are stored in thenonvolatile memory 17.

In FIG. 5B, information for the off-track data sectors may be registeredin, for example, the property of off-track as information for alternatesectors. For example, the information of the off-track data sectors maybe recorded in the nonvolatile memory 17 as the alternate sector area,due to occurrence of the off-track error, as indicated by the right sideof FIG. 5B.

During detecting occurrence of the off-track error, data sectors whichwould be writable if the off-track error does not occur are skipped.More specifically, the data sectors are skipped, as indicated by anarrow 56 in FIG. 5B. Then, data does not be written to data sector areasin the track B, which neighbor the data sectors A4 to A7. If theoff-track error ceases to be detected based on the servo data in theservo area 58, in order words, if it is ready to enable the write gateon, data are written to the magnetic disk 1 again. For example, data arewritten to data sectors B8 and B9.

FIG. 5C shows write processing with respect to the track C. As indicatedby an arrow in FIG. 5C, since the off-track error does not occur, dataare written to data sectors C0 to C9 in the track C.

Note that the off-track is assumed that in a direction of a track whichhas not been written yet by the shingled write recording method, asdescribed above. More specifically, the off-track indicates the track Cwhich has not been written yet in FIG. 5C. In FIG. 5B, the off-trackdata sectors are offset in the direction of the track C.

Note that the number of data sectors between neighboring servo areas(for example, between the neighboring servo areas 50 and 51) is notlimited to two, as shown in FIGS. 5A, 5B, and 5C.

Read processing upon occurrence of the off-track error corresponding tothe write processing described using FIGS. 5A, 5B, and 5C will bedescribed below with reference to FIGS. 6A, 6B, and 6C.

FIG. 6A shows read processing for the track A. On the track A, theoff-track error does not occur in the write mode. For this reason, dataare read from the data sectors A0 to A9 on the magnetic disk 1.

FIG. 6B shows read processing for the track B. In the read processingfor the track B, the off-track error has occurred in the write mode. Forthis reason, alternate data for data in areas where the off-track errorhas occurred (alternate sector areas) are read from the nonvolatilememory 17 based on, for example, the property of the off-track. Then,data in data sector areas other than the areas where the off-track errorhas occurred are read from the magnetic disk 1.

More specifically, after the data sectors B0 and B1 on the track B areread, data for the data sectors B2 to B7 including the off-track datasectors are read, wherein the off-track data sectors are stored in thenonvolatile memory 17. After that, data are read from the data sectorsB8 and B9 on the magnetic disk 1.

FIG. 6C shows read processing for the track C. In the read processingfor the track C, since the off-track errors do not occur in the writemode as in the case of the read mode for the track A, data are read fromthe data sectors C0 to C9 on the magnetic disk 1.

As described above, according to the first embodiment, even if anoff-track error has occurred upon writing data to the magnetic disk bythe shingled write recording method, these data are stored in thenonvolatile memory, thus continuously executing the write processing ofthe shingled write recording method. A data size stored in thenonvolatile memory is that corresponding to an off-track occurrenceperiod, that is, a data sector interval on the magnetic disk where theoff-track error has occurred. For this reason, a decrease in recordingdensity of data in the circumferential direction of the magnetic disk 1(longitudinal direction of the track) can be suppressed, and a useamount of the nonvolatile memory can also be suppressed.

Second Embodiment

The second embodiment will be described below with reference to thedrawings. Note that a description of the same components and functionsas those in the first embodiment will not be repeated.

In the second embodiment, if the off-track error has occurred in writeprocessing, data for one track are stored in the nonvolatile memory 17.Note that the data for one track are different from those for one track,which are stored in the DRAM 16, as described above with reference toFIG. 2. As the data for one track, which are described with reference toFIG. 2, read data for one track are stored in the DRAM 16 if theoff-track error does not occur. The data for one track stored in theDRAM 16 are used as the ITI cancellation data. On the other hand, as thedata for one track stored in the nonvolatile memory 17, data to bewritten to the magnetic disk 1 are stored in the nonvolatile memory 17in place of the magnetic disk 1 if the off-track error has occurred.

The second embodiment will be assumed a case in which write processingis executed by the shingled write recording method in which the degreeof overlap is higher than the first embodiment. For this reason, unlikein the first embodiment, the ITI cancellation function is used.

Write processing and read processing of the second embodiment will bepractically described below with reference to FIGS. 7A, 7B, 7C, 7D, 8A,8B, and 8C. Note that each of the second, third, and fourth embodimentsto be described below have different degrees of overlap between tracks,but FIGS. 7A, 7B, 7C, 7D, 8A, 8B, 8C, 9A, 9B, 9C, 10A, 10B, 10C, 11A,11B, 11C, 11D, 12A, 12B, 12C, and 12D illustrate tracks which overlapeach other to have the same degree of overlap, for the sake ofillustrative convenience.

FIGS. 7A, 7B, 7C, and 7D are views for explaining write processing uponoccurrence of the off-track error according to the second embodiment.

FIG. 7A shows write processing for a track A according to the secondembodiment. Although not shown, fixed data are written to a track A′before data is written to the track A. The track A is recorded on themagnetic disk 1 to overlap the track A′, as shown in FIGS. 3 and 4. Asin the first embodiment, the write head 10W moves in a direction of anarrow shown in FIG. 7A. Then, the write head 10W writes data to each ofdata sectors A0 to A9.

FIG. 7B shows write processing for a track B according to the secondembodiment. If it is determined that the off-track error has occurred,data for one track from the off-track data sector (data from a datasector B2 to a data sector C3) are stored in the nonvolatile memory 17.While data for one track are stored in the nonvolatile memory 17, writeprocessing with respect to a data sector interval on the magnetic disk1, which corresponds to the data for one track, is skipped, as indicatedby an arrow 70.

Note that data to be stored in the nonvolatile memory 17 may be that forthe number of tracks larger than one track if the cause of theoccurrence of the off-track error cannot be eliminated.

FIG. 7C shows write processing of data with respect to the track B ifthe data for one track are stored in the nonvolatile memory 17 and anon-track state is detected according to the second embodiment. In thiscase, for example, write processing of data with respect to the magneticdisk 1 is executed from a start position of a data sector (start datasector) at which the write gate is on after the magnetic disk 1 makesone revolution. More specifically, if the on-track state is detected,the write processing with respect to the magnetic disk 1 is restartedfrom data sectors (indicated by a data sector C4 (start data sector) anddata sector C5 in FIG. 7C) which follow the off-track data sectorinterval.

FIG. 7D shows write processing for a track C according to the secondembodiment. If the off-track error does not occur during the writeprocessing for the track B, data (data sectors C0 to C9) to be writtento the track C have already been stored on the data track B or thenonvolatile memory 17. For this reason, data to be written to a track D(not shown) are written to the track C, if the off-track error does notoccur.

Read processing upon occurrence of the off-track error corresponding tothe write processing described in FIGS. 7A, 7B, 7C, and 7D will bedescribed below with reference to FIGS. 8A, 8B, and 8C.

FIG. 8A shows read processing for the track A according to the secondembodiment. On the track A, the off-track error does not occur in thewrite mode. For this reason, data in the data sectors A0 to A9 on themagnetic disk 1 are read using data in a fixed data track as the ITIcancellation data.

FIG. 8B shows read processing for the track B according to the secondembodiment. In the read processing for the track B, the off-track erroroccurred in the write mode. For this reason, data in the data sectors B0and B1 are read using the data sectors A0 and A1 as the ITI cancellationdata. After that, the read processing of the off-track data sectors onthe magnetic disk 1 is slipped. Instead, data in the data sectors B2 toC3 including those on the off-track data sectors, which are stored inthe nonvolatile memory 17 are read. After that, data in the data sectorsC4 to C9 in the track B on the magnetic disk 1 are read using the datasectors A4 to A9 in the neighboring track as the ITI cancellation data.

FIG. 8C shows read processing for the track C according to the secondembodiment. In the read processing for the track C, the off-track errordoes not occur in the write mode. For this reason, data in the datasectors D0 to D9 on the magnetic disk 1 are read.

As for the ITI cancellation data upon reading the track C, the data inthe data sectors D0 and D1 are read using those on the data sectors B0and B1 as the ITI cancellation data. The data in the data sectors D4 toD9 are read using those on the data sectors C4 to C9 as the ITIcancellation data.

As for the data in the data sectors D2 and D3, data sectors neighboringthe data sectors D2 and D3 include off-track data sectors. For thisreason, the data in the data sectors D2 and D3 are read using those onalternate sectors B2 and B3, which are stored in the nonvolatile memory17, as the ITI cancellation data. Assume that data in the off-track datasectors on the magnetic disk 1 can be read. In this case, the data inthe off-track data sectors on the magnetic disk 1 can be used as the ITIcancellation data without using the data in the alternate sectors B2 andB3, which are stored in the nonvolatile memory 17, as the ITIcancellation data.

As described above, according to the second embodiment, even if theoff-track error has occurred upon writing data to the magnetic disk bythe shingled write recording method, data for one track are stored inthe nonvolatile memory 17. Thus, the write processing of the shingledwrite recording method can be continuously executed. Even if the degreeof overlap between neighboring tracks in the shingled write recordingmethod is high, that is, even if a recording density in the radialdirection of the magnetic disk 1 is high, interference components can becanceled using the ITI cancellation function. Then, a data playbackperformance as high as performance in a case that track pitches are notclosed up can be maintained. If data are rewritten to the magnetic disk1 after the off-track error has occurred, data can be written from aneighboring data sector in the same track as the off-track data sectors.For this reason, a decrease in recording density of data in thecircumferential direction (longitudinal direction) of the magnetic disk1 can be suppressed.

Third Embodiment

The third embodiment will be described below with reference to thedrawings. Note that a description of the same components and functionsas those in the first and second embodiments will not be repeated.

Compared to the first embodiment, the third embodiment is assumed a casein which write processing is executed by the shingled write recordingmethod with a higher degree of overlap than the first embodiment. Forthis reason, an ITI cancellation function is used, unlike in the firstembodiment. In the third embodiment, data to be stored in thenonvolatile memory 17 upon occurrence of the off-track error are notthose for one track, unlike in the second embodiment, but are those inthe off-track occurrence interval as in the first embodiment.

Write processing and read processing according to the third embodimentwill be practically described below with reference to FIGS. 9A, 9B, 9C,10A, 10B, and 10C.

FIGS. 9A, 9B, and 9C are views for explaining write processing uponoccurrence of the off-track error according to the third embodiment.

A description of FIG. 9A is the same as that of FIG. 5A described above,and will not be repeated.

FIG. 9B is a view for explaining write processing for a track B. In thethird embodiment, write processing is skipped for a data sector intervalin which a write gate is disabled. More specifically, after theoff-track error has occurred in data sectors B2 and B3, the writeprocessing with respect to the magnetic disk is skipped, as indicated byan arrow 90. Instead, data are stored in the nonvolatile memory 17 asalternate sectors B4 to B7.

A description of FIG. 9C is the same as that of FIG. 5C described above,and will not be repeated.

Read processing upon occurrence of an off-track error corresponding tothe write processing described using FIGS. 9A, 9B, and 9C will bedescribed below with reference to FIGS. 10A, 10B, and 10C.

A description of FIG. 10A is the same as that of FIG. 6A describedabove, and will not be repeated.

FIG. 10B is a view for explaining read processing for the track B. Afterdata sectors B0 and B1 are read, read processing of the off-track datasectors is slipped. Data in the off-track occurrence interval (thatindicated by a doted line in FIG. 10B) which does not include the datasectors B2 and B3 are read, so as to use the data in the off-trackoccurrence interval as neighboring data upon reading a track C. Then,the read data are temporarily stored in a storage medium such as theSRAM, the DRAM 16, or the nonvolatile memory 17. As data in theoff-track interval, data of alternate data sectors B2 to B7 in thenonvolatile memory 17 are read.

FIG. 10C shows read processing for the track C. Upon reading datasectors C2 and C3, alternate data sectors B2 and B3 in the nonvolatilememory 17 are used as the ITI cancellation data. However, if the datasectors B2 and B3 can be read, they may be used. Upon reading datasectors C4 to C7, data in data areas 1000 to 1003, indicated by dottedlines, that is, those of the off-track occurrence interval which aretemporarily stored upon reading the track B and do not include the datasectors B2 and B3, are used as the ITI cancellation data.

For example, in case that the degree of overlap of the shingled writerecording method is 50%, half of the track A overlaps half of the trackB. Furthermore, half of the track C overlaps half of the track B. Forthis reason, the data areas 1000 to 1003 cannot be read by the read head10R. Such a case is applied to not the third embodiment but the fourthembodiment.

As described above, according to the third embodiment, even if theoff-track error has occurred upon writing data to the magnetic disk 1 bythe shingled write recording method, data for one track are stored inthe nonvolatile memory 17. Thus, the write processing of the shingledwrite recording method can be continuously executed. Using the ITIcancellation function, interference components can be canceled. Then, adata reproduction performance as high as that when track pitches are notclosed up by the shingled write recording method can be maintained. Adata size to be stored in the nonvolatile memory 17 is thatcorresponding to an off-track occurrence period, that is, a data sectorinterval on the magnetic disk 1 where the off-track error has occurred.For this reason, a decrease in recording density of data in thecircumferential direction (longitudinal direction) of the magnetic disk1 can be suppressed, and a use amount of the nonvolatile memory 17 canalso be suppressed.

Fourth Embodiment

The fourth embodiment will be described below with reference to thedrawings. Note that a description of the same components and functionsas those in the first to third embodiments will not be repeated.

The fourth embodiment is assumed a case in which data in the data areas1000 to 1003 shown in FIG. 10C cannot be read normally, that is, cannotbe read normally to a level at which they can be used as the ITIcancellation data in the read processing of the third embodiment. Insuch a case, in the fourth embodiment, fixed pattern data which can beused as the ITI cancellation data are written in a track which neighborsthe data areas 1000 to 1003.

Write processing and read processing of the fourth embodiment will bepractically described below with reference to FIGS. 11A, 11B, 11C, 11D,12A, 12B, 12C and 12D.

FIGS. 11A, 11B, 11C, and 11D are views for explaining write processingupon occurrence of the off-track error according to the fourthembodiment.

Descriptions of FIGS. 11A and 11B are the same as those of FIGS. 9A and9B described above, and will not be repeated.

FIG. 11C is a view for explaining write processing for a track C. Fixedpattern data (indicated by “fixed a” to “fixed f” in FIG. 11C) arewritten in data sectors in the track C, which neighbor the off-trackoccurrence interval (indicated by data sectors B2 and B3 and data areas1000 to 1003 in FIG. 11C).

The fixed pattern data are those of predetermined repetitive patterns orthe like. The fixed pattern data may be the same as fixed data in thefixed data track described above with reference to FIG. 3, but they maybe different data. The fixed pattern data are those which are written indata sectors which neighbor the off-track occurrence interval. On theother hand, the fixed data are those, which are written first by theshingled write recording method, and are required to read data in atrack A using the ITI cancellation function in the write order by theshingled write recording method.

FIG. 11D is a view for explaining write processing for a track D whichdata is written after being written to the track C by the shingled writerecording method. As indicated by an arrow in FIG. 11D, data are writtenin data sectors D0 to D9 without causing the off-track error.

Read processing upon occurrence of the off-track error corresponding tothe write processing described using FIGS. 11A, 11B, 11C, and 11D willbe described below with reference to FIGS. 12A, 12B, 12C, and 12D.

Descriptions of FIGS. 12A and 12B are the same as those of FIGS. 10A and10C described above, and will not be repeated.

FIG. 12C is a view for explaining read processing for the track C. Readprocessing of data in data sector areas indicated by “fixed a” to “fixedf” are slipped.

FIG. 12D is a view for explaining read processing for the track D. Datain the data sectors D2 to D7 are read, using the ITI cancellationfunction which uses the predetermined neighboring fixed pattern data(“fixed a” to “fixed f”).

As described above, according to the fourth embodiment, even when theoff-track error has occurred upon writing data to the magnetic disk 1 bythe shingled write recording method, the write processing of theshingled write recording method can be continuously executed by storingdata in the nonvolatile memory 17. Even if the degree of overlap betweenneighboring tracks in the shingled write recording method is high, thatis, even if the recording density in the radial direction of themagnetic disk 1 is high, interference components can be canceled usingthe ITI cancellation function. For this reason, a data playbackperformance as high as that when track pitches are not closed up by theshingled write recording method can be maintained.

Fifth Embodiment

The fifth embodiment will be described below with reference to thedrawings. Note that a description of the same components and functionsas those in the first to fourth embodiments will not be repeated.

The fifth embodiment relates to read processing and write processing inthe shingled write recording method as a combination of some of fourmodes corresponding to the first to fourth embodiments.

The four modes will be described first with reference to FIG. 13.

Elements of FIG. 13 will be explained first.

“Write processing at off-track error timing” indicates whether or notwrite processing upon occurrence of the off-track error is to beexecuted while data are written to the magnetic disk 1 by the shingledwrite recording method. As shown in FIG. 13, in all the four modes, evenif the off-track error has occurred, the write processing iscontinuously executed without being interrupted.

“ITI cancellation function” indicates whether or not to use the ITIcancellation function. As for the three modes other than the mode 1corresponding to the first embodiment, the ITI cancellation function isused.

The term “tracks per inch” (TPI) indicates a unit of a track density onthe magnetic disk 1, and the number of tracks per inch in the radialdirection of the magnetic disk 1. The TPI will be described below usingthe mode 3 corresponding to the third embodiment as a reference.

In mode 1, since the degree of overlap between tracks is low, the valueof the TPI in the mode 1 is low.

In the mode 3 corresponding to the third embodiment, if the degree ofoverlap between tracks is large, data in the off-track occurrenceinterval cannot be read from the magnetic disk 1 as the ITI cancellationdata. On the other hand, in the mode 2, even if the degree of overlapbetween tracks is 50% or more, since data in the off-track occurrenceinterval are stored in the nonvolatile memory 17, the data in theoff-track occurrence interval can be used as the ITI cancellation data.For this reason, in the mode 2, a larger value of the TPI than the mode3 can be set.

In the mode 4, the fixed pattern data can be used as the ITIcancellation data. For this reason, the degree of overlap between trackscan be increased, and a larger value of the TPI than the mode 3 can beset, in the mode 4.

“Data efficiency in circumferential direction” indicates efficiency ofdata recording in the circumferential direction of the magnetic disk 1.That is, if data are effectively recorded in the circumferentialdirection, the data efficiency in the circumferential directionincreases. In FIG. 13, in the mode 4, write processing for the off-trackoccurrence interval is skipped, and the fixed pattern data are writtenin the track which neighbors the off-track occurrence interval. For thisreason, the data efficiency in the circumferential direction in the mode4 is lower than those in the modes 1 to 3.

“NAND use amount” indicates amount used for NAND flash memory which isone of examples of the nonvolatile memory 17. The NAND use amount willbe described below using the mode 1 and the mode 3 corresponding to thefirst embodiment and the third embodiment as a reference.

In the mode 1 and the mode 3, data corresponding to an interval that thewrite-gate is disabled (as referred to a write-gate disabled interval,below) are stored in the nonvolatile memory 17.

Next, in the mode 4, data corresponding to only the write-gate disabledinterval, or data corresponding to the write-gate disabled interval anddata sectors which neighbor the write-gate disabled interval, is storedin the nonvolatile memory 17. Note that data corresponding to datasectors which neighbor the write-gate disabled interval are theaforementioned fixed pattern data. In this embodiment, the fixed patterndata is written to the magnetic disk 1, and may or may not be stored inthe nonvolatile memory 17.

In the mode 2, since data for one track are stored in the nonvolatilememory 17, the NAND use amount is larger than those in modes 1, 3, and4.

Write processing and read processing according to the fifth embodimentwill be described below with reference to FIGS. 14 and 15.

FIG. 14 is a flowchart showing an example of the write processingsequence according to the fifth embodiment.

The write processing starts by data to be written to the magnetic disk 1are sent from the host system 20 to the interface controller 13, or thelike.

The interface controller 13 determines in block 1400 whether or not touse the ITI cancellation function. If the ITI cancellation function isused, the interface controller 13 writes the fixed data track to themagnetic disk 1 in block 1402, and the process advances to block 1404.If it is determined in block 1400 that the ITI cancellation function isnot used (the mode 1), since the fixed data need not always be written,the process advances to block 1404. Note that processing in block 1402is an example of processing if the ITI cancellation function is notused, and the fixed data may be written in advance to the magnetic disk1 before the beginning of the write processing.

Note that whether or not to use the ITI cancellation function in block1400 may be selected by the user. Alternatively, prior to the beginningof the write processing, if, for example, a bit error rate of read datais high, it may be set in advance to use the ITI cancellation function.

The off-track determination module 27 a determines in block 1404 basedon the off-track determination signal whether or not the off-track errorhas been detected. If the off-track error does not be detected, theprocess advances to block 1414 to continue the write processing of datawith respect to the magnetic disk 1. If it is determined that theoff-track error has been detected, the write data selector 21 adetermines in block 1406 whether or not data to be stored in thenonvolatile memory 17 are those for one track. If data for one track areto be stored in the nonvolatile memory 17 (the mode 2), the processadvances to block 1412, and the write data selector 21 a executesprocessing required to store the data for one track in the nonvolatilememory 17.

If data for one track are not to be stored in the nonvolatile memory 17(the mode 1, the mode 3, and the mode 4), the process advances to block1408. In block 1408, the write module 21 executes processing required toskip the write processing in the off-track occurrence interval of themagnetic disk 1, and the write data selector 21 a executes processingrequired to write data corresponding to the off-track occurrenceinterval in the nonvolatile memory 17 as alternate data. The processthen advances to block 1410, and the write data selector 21 a determineswhether or not the off-track error ceases to be detected. If theoff-track error ceases to be detected, the write processing of data withrespect to the magnetic disk 1 is restarted in block 1414.

Finally, the interface controller 13 determines in block 1416 whether ornot the write processing of all data sent from the host system 20 iscomplete. If the write processing is not complete yet, the processreturns to block 1404.

FIG. 15 is a flowchart showing an example of the read processingsequence according to the fifth embodiment.

Initially, for example, if a read request of data from the magnetic disk1 is received from the host system 20, the read processing starts.

The read module 22 determines in block 1500, based on the property ofthe off-track and the like, whether or not data sectors (off-trackoccurrence interval) where the off-track error occurred and whichinclude write-skipped data sectors, are to be read. If the off-trackerror is detected, data are read from the nonvolatile memory 17 in block1508 (the modes 1 to 4).

If the off-track occurrence interval is not read in block 1500, theprocess advances to block 1502 to determine whether or not to use theITI cancellation function. If the ITI cancellation function is used (themode 1), the read module 22 executes processing required to read datafrom the magnetic disk in block 1506.

If the ITI cancellation function is used (the mode 2, the mode 3, andthe mode 4), it is determined in block 1503 whether or not the fixeddata has already been written. If the fixed data has already beenwritten (the mode 4), the read processing of data sectors in which thefixed data are written is slipped in block 1505. Next, in block 1504,data which have already been read from the magnetic disk 1 and aretemporarily stored in the DRAM 16, or data which are stored in thenonvolatile memory 17 and in correspondence with the off-trackoccurrence interval, are used as the ITI cancellation data. Then, dataon the magnetic disk 1 are read while canceling interference componentsfrom data sent from the magnetic disk 1. Finally, the interfacecontroller 13 determines, based on a read request or the like from thehost system 20, whether or not the read processing of all data iscomplete.

As described above, according to the fifth embodiment, some of the fourmodes of the read processing and write processing of the shingled writerecording method are combined, thus switching the ITI cancellationfunction. Also, the mode to be used can be switched according to the useamount of the nonvolatile memory, the use efficiency of the magneticdisk, and the like.

As described above, according to the first embodiment to the fifthembodiment, the write processing based on the shingled write recordingmethod can be executed without lowering a write performance with respectto the magnetic disk by the shingled write recording method (that is,without lowering variations of the write performance based on theshingled write recording method). For example, in case that the writegate is disabled and the write processing with respect to the magneticdisk 1 cannot be executed, data sectors which follow the off-trackoccurrence data sectors are used as the alternate data sectors, and datain the off-track occurrence data sectors are written in the nonvolatilememory 17, thus suppressing a write performance drop. Since thenonvolatile memory 17 is used, the write processing is not delayedalthough the write processing with respect to the magnetic disk 1 isinterrupted, and it can be expected that the write processing iscomplete within a predetermined time period. Also, since the nonvolatilememory 17 is used, even if the off-track error has occurred, data in theoff-track occurrence interval need not be written again (overwritten) toidentical data sectors of the magnetic disk 1. For this reason, thenumber of writings to the magnetic disk 1 can be suppressed. That is,the write processing need not be interrupted, if the off-track error hasoccurred, until the magnetic disk 1 makes one revolution and until thewrite processing for next data sectors which follow the off-trackoccurrence data sectors is ready to be executed. Since the number ofwritings is suppressed, the influence of read processing due to magneticinterference on neighboring tracks can be eliminated.

Note that in any of the first embodiment to the fifth embodiment, forexample, a hybrid hard disk (HDD) which incorporates a high-speed andlarge-capacity nonvolatile memory, or the like, may be applied.

The various modules of the systems described herein can be implementedas software applications, hardware and/or software modules, orcomponents in one or more computers, such as servers. While the variousmodules are illustrated separately, they may share some or all of thesame underlying logic or code.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk apparatus comprising: a magneticdisk comprising a first data sector, first data being recorded in thefirst data sector while neighboring tracks partially overlap each other;a nonvolatile memory; a determination module configured to determinewhether off-track write occurs on the first data sector during a writemode; a write module configured to write the first data in thenonvolatile memory if the determination module determines that theoff-track write occurs on the first data sector; and a read moduleconfigured to read the first data from one of the magnetic disk and thenonvolatile memory based on a determination result of the determinationmodule.
 2. The apparatus of claim 1, wherein the determination moduledetermines whether data sectors following the first data sector on themagnetic disk comprise off-track write occurrence data sectors, and thewrite module is further configured to write second data corresponding tothe off-track write occurrence data sectors from the first data sectorto a second data sector that is one of the data sectors after thedetermination module determines if the off-track write occurs on thefirst data sector, said writing occurring until the determination moduleis configured to determine if the off-track write occurs on the seconddata sector.
 3. The apparatus of claim 2, wherein the write module isconfigured to skip write processing to the second data sector, and theapparatus further comprises a noise cancellation controller configuredto cancel noise generated between the tracks neighboring on the magneticdisk using the off-track write occurrence data sectors.
 4. The apparatusof claim 2, wherein the write module is configured to skip the writeprocessing to the second data sector, and to write fixed data in datasectors which neighbor the off-track write occurrence data sectors, andwherein the apparatus further comprises a noise cancellation controllerconfigured to cancel noise generated between tracks neighboring on themagnetic disk using the fixed data.
 5. The apparatus of claim 2, furthercomprising a noise cancellation controller configured to execute controlfor cancelling noise generated between tracks neighboring on themagnetic disk using data written in the nonvolatile memory.
 6. Theapparatus of claim 1, wherein the write module is configured to writedata for one round of a track on the magnetic disk in the nonvolatilememory, and to execute write processing with respect to a second datasector following the first data sector without skipping write processingto the second data sector, if the determination module is configured todetermine that the first data sector comprises the off-track writesector.
 7. The apparatus of claim 6, further comprising a noisecancellation controller configured to execute control for cancellingnoise generated between tracks neighboring on the magnetic disk usingdata written in the nonvolatile memory.
 8. The apparatus of claim 1,further comprising a noise cancellation controller configured to executecontrol for cancelling noise generated between tracks neighboring on themagnetic disk using data written in the nonvolatile memory.
 9. A readand write control method in a magnetic disk apparatus comprising amagnetic disk and a nonvolatile memory, the magnetic disk comprising afirst data sector with first data recorded in the first data sectorwhile neighboring tracks partially overlap each other, the methodcomprising: determining whether the off-track write occurs on the firstdata sector during a write mode to obtain a determination result;writing the first data in the nonvolatile memory if it is determinedthat the off-track write occurs on the first data sector; and readingthe first data from one of the magnetic disk and the nonvolatile memorybased on the determination result.
 10. The method of claim 9, whereindetermining whether the off-track write occurs on the first data sectorduring a write mode further comprises determining whether data sectorsfollowing the first data sector on the magnetic disk comprise off-trackwrite occurrence data sectors, and wherein the writing further compriseswriting second data corresponding to the off-track write occurrence datasectors from the first data sector to a second data sector that is oneof the data sectors, after the determining determines if the off-trackwrite occurs on the first data sector, the writing occurring until thedetermining determines that the off-track write occurs on the seconddata sector.
 11. The method of claim 10, wherein the writing comprisesskipping write processing to the second data sector, and the methodfurther comprises canceling noise generated between the tracksneighboring on the magnetic disk using the off-track write occurrencedata sectors.
 12. The method of claim 10, wherein the writing comprisesskipping the write processing to the second data sector, and writingfixed data in data sectors which neighbor the off-track write occurrencedata sectors, and wherein the method further comprises canceling noisegenerated between tracks neighboring on the magnetic disk using thefixed data.
 13. The method of claim 9, wherein the writing compriseswriting data for one round of a track on the magnetic disk in thenonvolatile memory, and executing write processing with respect to asecond data sector following the first data sector without skippingwrite processing to the second data sector, if the determining comprisesdetermining that the first data sector comprises the off-track writesector
 14. The method of claim 9, further comprising executing controlfor cancelling noise generated between tracks neighboring on themagnetic disk using data written in the nonvolatile memory.
 15. Anapparatus comprising: a controller configured to: determine whether theoff-track write occurs on a first data sector on a magnetic disk duringa write mode to obtain a determination result, the first data recordedin the first data sector while neighboring tracks partially overlap eachother; write the first data in a nonvolatile memory if it is determinedthat the off-track write occurs on the first data sector; and read thefirst data from one of the magnetic disk and the nonvolatile memorybased on the determination result.
 16. The apparatus of claim 15,wherein the controller is further configured to determine whether datasectors following the first data sector on the magnetic disk compriseoff-track write occurrence data sectors, and to write second datacorresponding to the off-track write occurrence data sectors from thefirst data sector to a second data sector that is one of the datasectors, after determining if the off-track write occurs on the firstdata sector, the writing occurring until the controller determines thatthe off-track write occurs on the second data sector.
 17. The apparatusof claim 16, wherein the controller is further configured to skip writeprocessing to the second data sector, and to cancel noise generatedbetween the tracks neighboring on the magnetic disk using the off-trackwrite occurrence data sectors.
 18. The apparatus of claim 16, whereinthe controller is further configured to skip the write processing to thesecond data sector, and to write fixed data in data sectors whichneighbor the off-track write occurrence data sectors, and wherein thecontroller is further configured to cancel noise generated betweentracks neighboring on the magnetic disk using the fixed data.
 19. Theapparatus of claim 15, wherein the controller is further configured towrite data for one round of a track on the magnetic disk in thenonvolatile memory, and execute write processing with respect to asecond data sector following the first data sector without skippingwrite processing to the second data sector, if the controller determinesthat the first data sector comprises the off-track write sector
 20. Theapparatus of claim 15, wherein the controller is further configured toexecute control for cancelling noise generated between tracksneighboring on the magnetic disk using data written in the nonvolatilememory.